Maria Neira compared the crisis over air pollution to the asbestos scandal, in which governments were accused of failing to act quickly enough to save lives despite knowing the risks.

In an interview with The Times, the director of the World Health Organisation’s Department of Public Health, Environmental and Social Determinants of Health, said that delaying action on the sources of air pollution, such as road traffic and wood burning in urban areas, would cost thousands of lives.

She praised this newspaper’s Clean Air for All Campaign and supported our call for sales of new petrol and diesel cars to be banned by 2030.

Dr Neira said that she was particularly concerned by the damage air pollution does to children’s lungs and brains.

“We know that, 15 years from now, those who have been exposed to high levels of air pollution will suffer major consequences in their immune, digestive and nervous systems and their respiratory systems will be deficient. If this is the society we are preparing for our children we are all very irresponsible.”

She said that toxic air cut short the lives of 40,000 people a year in the UK and 400,000 across Europe and governments and local authorities needed to act quickly to tackle it “even if the measures are not very popular”.

“If you postpone [action] by one day it might be hundreds of lives,” she said.

“If you postpone it by one year it might be thousands of lives plus the cost of the health system and the cost in terms of quality of life from living with asthma.”

She urged politicians to think about the consequences to people’s health of delaying making tough decisions, such as reducing traffic in cities and investing in measures to encourage cycling.

“This is something every politician should ask himself or herself every morning if they say, ‘Instead of 2030 I will do it in 2040’. They should ask the WHO what does that mean in terms of affecting the health of the people and how many new cases of lung cancer. We can calculate that.

“The question here is how many of those lives, or reduction in quality of life, are you ready to absorb. They should inform the public of those consequences and face the risk of losing votes.”

She predicted that politicians who failed to act could be forced to defend their decisions in court.

“Look at the case of asbestos. At one point some politicians were taken to court — the ministry of health in France — because they were accused of [knowing] about the risk of asbestos and [they] didn’t do enough.

“I have the feeling in a few years from now this will be the case [for air pollution] and no politician will be able to say I didn’t know because we all knew and this information has been well-established.”

She added: “There are legal groups already working on this. They have patients and people who lost family members. I can perfectly see the scenario of politicians being accused by our citizens saying, ‘You knew it, you didn’t do anything, therefore you are responsible for the number of deaths that have occurred.’”

She referred to the High Court ruling last month that a new inquest should be held into the death of a nine-year-old girl who suffered a fatal asthma attack believed to have been linked to illegal levels of air pollution near her home in London.

“Look at the case of Ella Kissi-Debrah, this might be a beginning. If you talk to legal groups, the number of cases now going to court is increasing. It might be that in the next few years it increases exponentially.”

The government has already been defeated three times in court by Client Earth, the campaign group which successfully argued that air quality plans were inadequate. The group is now considering bringing new cases against the government and local authorities over illegal levels of nitrogen dioxide pollution on hundreds of roads.

Dr Neira said politicians who believed that taking tough action on air pollution was too expensive should consider the costs of not acting. In 2016 the Royal College of Physicians estimated the costs to individuals, the health service and economy to be more than £20 billion a year in the UK.

“The health system is paying an incredible price at the moment to treat patients because we are talking about chronic diseases and those are very, very costly,” she said. “If you include that cost in your equation then the investment will be recovered immediately by the savings in your health system.”

She urged the car industry to plan a much faster switch to electric cars and suggested they were trying to prolong sales of petrol and diesel cars.

“They are not switching fast enough. They don’t sell fuels they sell the car so they should make the switch as soon as possible. Otherwise they will be responsible for this air pollution crisis.

“If they want to still sell mobility they need to stop selling fossil fuel. They will then be perceived as heroes rather than the guilty ones.”